1. Field of the Invention
The present invention relates to a heat radiating apparatus for a semiconductor device and, more particularly, a heat radiating apparatus for a semiconductor device which cools a semiconductor device mounted on a circuit board by means of a radiator.
2. Description of the Related Art
Recently, semiconductor integrated circuits have been more highly integrated and their operation has become faster as the function of electronic devices has become higher and greater density mounting has been realized. As a result, the power requirement has increased and the heating value of a semiconductor device has also increased. Therefore, a heat radiating apparatus is needed which efficiently radiates heat from the surface of a semiconductor device.
There are two conventional types of heat radiating apparatus for a semiconductor device in which an external radiator is brought into contact with the semiconductor device. For one type, a radiator having a plurality of heat radiating fins is fixed to the stud section with a heat conductive adhesive on the top surface of the semiconductor device mounted on a circuit board. For the other type, a radiator having a similar construction is fixed to the top surface of the semiconductor device by means of fixing hardware. For example, the fixing hardware, divided into two pieces, is inserted between the heat radiating fins of the radiator, and the end surface of the stud section is pushed onto the top surface of the semiconductor device, so that the fixing hardware is fixed to the circuit board. The fixing is performed by screwing or hooking.
The heat radiators described above, however, have the following problems. In the case of the former type, an adhesive is present between the semiconductor device and the radiator. Even though the adhesive is heat conductive, the heat conductivity is low as compared with the case where the semiconductor device is in direct contact with the radiator. Therefore, the heat radiation efficiency is lowered. Moreover, since the heat expansion efficiency differs between the radiator and the heat conductive adhesive, thermal stress is produced at high temperatures, thereby a stress is given to the top surface of the semiconductor device. In addition, the temperature cycle results in the deterioration or breakage of the adhesive, thereby resulting in the radiator coming off the semiconductor device,
In the case of the latter type, there is a possibility that the radiator can be installed in such a manner as to slightly float or be tilted with respect to the top surface of the semiconductor device. In this case, the contact area is significantly decreased, and the heat conductivity is greatly lowered because the heat conduction from the semiconductor device to the radiator is carried out by the contact only. In fixing the radiator to the semiconductor device, a pressure higher than necessary may be applied to the semiconductor device from the radiator. In this case, there is a possibility of damage to the semiconductor device.